Process for refining lead and its alloys



Patented Feb. 27, 195i UNI PROCESS FORREFINING LEAD AND ITS ALLOYS Max Meyer, New York, N. Y., assi'gnor to Meyer Metallurgical Corporation, New York, N. Y.

N Drawing. Application April 12, 1949, Serial No. 87,111

4 Claims.

This invention relates to the purification of lead and lead alloys containing tin and antimony, which are the so-called white metals; it pertains specifically to the collective removal, from lead and its alloys with tin and antimony of certain frequent impurities such as arsenic, copper, iron, nickel and sulfur.

A Variety of methods has been developed for the purification of lead and its alloys and the selection of the particular refining method is generally influenced by the dependent upon the nature of these impurities and the quantities present.

If, for instance, copper or iron is contained in the lead or its alloys purification is primarily carried-out in a furnace or a smelting pot by liquation whereby the larger percentage of these impurities is obtained in the resulting coppery by-products; the final refi ning operation is then performed in a smelting pot to remove the copper or iron still present by sulphurization using elementary sulphur or alkali sulfides or sulfates as a reageant.

Other impurities, such as arsenic, which is often present in lead would not be affected by this practice; therefore, upon removal of the copper or iron another refining process is required for the removal of arsenic; this is often done at a high temperature by oxidation and volatization in a furnace or by a treatment with caustic soda in a smelting pot.

The removal of nickel by sulphurization offers a difficult problem because of the low afiinity of nickel to sulphur, which ranges far behind that of the affinity of lead to sulphur.

In conformity with another method, which after the elimination of the bulk of the copper from lead by liquation or sulfurization removes very small quantities of copper still present, the lead is admixed with sodium hydroxide and elementary reagents for the sulphurization of the copper. The amount of sulphur used in accordance with this method is the multiple of the quantity of copper still present in the lead; as a consequence thereof not only the copper but also a large quantity of lead is sulphurized.

All these known methods have one common characteristic feature. They are based on the conversion of certain impurities into compounds,

7 analysis.

1y molecular relationship to the contaminations; a multiplicity of operations are unavoidable. The performance of these customary purification processes requires the maintenance of accurately controlled working conditions. The quantity and the character of the contaminations must be determined by analysis before the work is commenced as the admixture of the purifying agents is controlled in conformity with the result of the In spite of all this a guarantee is not given for a successful performance of purely chemical reactions initiated by the admixture of the refining agents. Moreover, most of these methods are expensive; for instance, an economically satisfactory purification in melting kettles is not achieved if higher percentages of impurities are present. Layers of skimmings and dross must be drossed or skimmed-off before the commencement of the refining operation whereby great quantities of the lead and its alloying ing pot. Moreover, the known refining processes for instance, sulfides by chemical reaction Within accordingly defined proportions or they in volve considerable disadvantages, for instance,

large quantities of residues. admixtureof the purifying agents-inapracticaldo not permit of the collective removal of heterogeneous elements.

It is an important object of this invention to successfully refine lead and white metals and to remove from the same bythe same agent all impurities comulatively such as, particularly, arsenic, copper, iron, nickel and sulphur.

Another important object of this invention is the removal of arsenic. This manipulation hitherto required a separate operation either by oxidation and volatization or by a treatment with caustic soda. In conformity with this invention arsenic is removed in most cases by the same agent and simultaneously with the other impurities.

Itiisa further object of this invention to effect a removal of the impurities mentioned above and of others in one and the same operation with quantity of the impurities present is a further important object of this invention.

'It is a highlyimportant object of this invention to' effect the elimination of the impuritiesfrom the molten metalbath without the exercise of chemically defined reactions but apparently by catalytic action.

A further object of this invention is to separate the molten metal and its impurities immediately upon its contact with the purifying agents.

It is also an object of this invention to effect the removal of the impurities as a highly concentrated and essentially metallic dross whereby the yield of the refined metal is correspondingly increased.

It is another object of this invention to render the refining of the metal independent upon an analysis of the initial charge or a control analysis during the operation and to thus save working time and costs.

A further object of this invention is the maintenance of equal and unchanged operative conditions yielding a metal of a surprisingly high purity and the exclusion of hazards and insecurities with regard to the progress of the purification.

A most important object of this invention is the introduction into practice of a new technical conception as a basis for a metal refining procedure.

It is another important object of this invention to introduce a process, which due to its simplicity, low operation costs, time saving and efficiency is superior to any other known lead refining procedure.

With the above recited and other objects in view which will become apparent as this specification proceeds, the invention is based on the surprising discovery that an exceedingly small amount of a mixture of alkali hydroxide and sulphur effecting an immediate intensive action which quickly separates the impurities from lead and its alloys the latter being removed from the bath in the form of a mainly metallic dross. The admixture of the refining agents at a ratio of 0.1 to 0.3 per cent of the weight of the charge is generally satisfactory in order to obtain a completely refined metal; somewhat higher amounts of the reagents may be added if the metal to be refined is derived, for instance, from a reverberatory or blast furnace; in such a case the quantity of the reagents may be increased to 0.5 per cent and eventually even to about 1 per cent. However, a greater quantity of the reagents does not influence the performance of the catalytic action as such.

The refining operation is carried-out in one single operation and in the plurality of cases in a melting kettle.

The liquified metal bath is vehemently stirred at the commencement of the refining operation without removal of any dross, whereby a. center vortex is produced surrounding the shaft of the stirrer. Th refining agent is gradually entered into the vortex. Upon the admixture of the first portion of the refining agent to the vehemently stirred metal bath a clearly recognisable retardation occurs of the metal movement and a light colored scum appears on the surface of the same. The center vortex gradually fills up. Admixture of further refining reagents is interrupted until the scum has disappeared from the surface of the bath and the vortex surrounding the stirrer becomes again visible; this takes about one to two minutes whereupon the admixture of the purifying agent is continued until a definite layer of the mush has formed on surface of the bath.

The mush contains the impurities separated from the molten metal and a considerable proportion of the latter; the next step of this process is the separation from the mush of the impurities and the adhering mother metal.

Any conventional method may be used for this purpose; the admixture of carbonaceous substances such as coal dust or saw dust has been found to be satisfactory insofar as a dry finely pulverulent dross results, which is easily removed from the bath.

After the removal of the dross the stirrer should be again set in motion in order to ascertain whether further mush will form, which also should be converted into dross. The appearance of a bright metal surface indicates that the impurities have been eliminated.

This surprisingly quick and complete refining action in conformity with this invention is not the result of a chemical reaction between the lead impurities and the added reactants because the quantity of the latter is far too small to remove the impurities in the form of salts or other combines with the purifying agents; the fact is that by the initial reaction of the added substances with certain impurities apparently a strong catalytic action is originated, whereby the impurities are separated in a metallic state. This intensive catalytic action is evident when a sample, shortly after the reagents have been stirred into the bath, is taken from the moving metal and poured into a mold; the solidified bar has a bright surface appearance; if the initial charge contains a substantial proportion of copper, for instance, 2 per cent next to other impurities an analysis of this sample bar already may only show 0.02 per cent Cu; it is understood however that the refining procedure is not completed at this stage; on the other hand, the metallic character of the dross is recognizable by the naked eye from the abundance of shiny metallic particles. The catalytic action is greatly assisted by the intimate contact of the energetically agitated bath particles with the added substances. The fact that the dross mainly consists of metallic components is convincingly proven by its reddish color if copper was present in the initial charge up to a certain amount. If this impurity is present in a larger quantity the dross is infiltrated with red crystals and scales; this indicated that the impurities have been mainly removed as metals. This removal is not restricted to the customary lead contaminations.

If tin is present in the lead or its alloys it is not influenced by this refining procedure; therefore, the tin contents of the refined metal differ not at all or very slightly from that of the initial tin content and is raised if the impurities are removed accordingly. The same is more or less true with antimony which is hardly affected by this refining procedure; there is a dilference between antimony and tin insofar as antimony has a greater tendency than tin to oxidize by the stirring action and therefore, greater amounts of antimony might be present in the dross if the initial lead contained a high proportion thereof.

The invention characterizes an important advantage over the art with regard to tin because in accordance with customary refining processes a considerable percentage of tin present in lead or its alloys is oxidized and carried into the dross. It is a remarkable feature of the invention that the retention of tin in the lead is increased with the percentage of tin in the initial charge.

The invention may be preferably carried-out in a melting kettle provided with a strong mechanical stirrer; the quantity of dross resulting from the instant treatment is considerably smaller than with customary refining processes where it has been found impracticable to refine lead and white metals containing more than about 2 per cent impurities in a melting kettle. It, therefore, is animportant advantage of the in' vention that metals containing high quantities of impurities can be successfully refined in a kettle and that the usual removal of large quantities of 0 or aprsrosiniateiynair of thereagentsan arsenic contents was'found of 004%, after -rninutes, of 0.01% and afterfurther- 15 minutes-of 0.000%.

dross prior to the start of the refining operation 5 10,060 pounds of white metal scrap were can be eliminated. Only if the amount of immolten in a smelting pot; thecomposition of the purities is very high then it may be preferable molten metal at the start of the'operation was:

Sii Sb 011 As Ni zn a Pb Per cent Per cent Per cent Per cent Per cent Per cent 12.05 13 1. 0s 0. 05 0.03 m 0.18 Balance to carry-out the invention in a Walled-up furmixture or pounds NaOH and 12 pounds S nace having a deep sole. The admixture of the was added. The treatment was carried out" as reactants and the progress of'the refining action described previously; 7 7 would, in this case, be the same as in a melting After the eoinpletionofthe refining procedure kettle. The separation of the scum can be caL-r- 20 390' pounds of dross were skimmed on and 9710 ried out in the same manner or the furnace may pounds refined metal resulted of the following be pierced at the bottom and the remaining scum analysis: then treated in any usual manner by a sweating or other suitable method. 8 Sb Pb It is emphasized that the success of this inn vention and the quantity of the refining admiX- PM as 1 Percent ture is independent upon the quantity of the 12. 25 12' Balance impurities present and uponthe relationship'of the constituents in the admixture.

The following examples will further explain Example 4 the nature and the characteristics of my invention without, however, restricting the same to pounds of alead allwpbtamed fromrthe the given figures as far as the quantities of the Smeltmg W metal dross m reverberatory admixture added, are concerned. a e w he d n @smelting e composition of the molten-metal at the start of Example 1 therefining operation was, as follows:-

Approximately 50 tons of an impure lead con taining Sn Sb Cu As Fe 7 w Per cent I Per cent Per cent Per cent I Per cent Sb As Cu Ph 4. 70 13.80 0.70 0.03 0.10

r tgfg 3 Balance The dross which appeared on the surface of 4 the metal upon melting the same was not removed. The refining operation was carried out Was treated Wlth 240 p n NaOH 60 in the same manner, as explained in the descrippounds S of the reactants; .a refined metal was ti I recovered havmg thefollo'wmg analysis: The quantity of reagents added was 15 pounds NaOH and 6 pounds S; the quantity of dross Sb As on mad removed after the completion of the refining pro- A. cedure was 370 pounds.- Perm Pmm Percent 9, 830 pounds of refined metal were recovered 0.11s 0. 0018 0.002 Balance having the following compos1t1on:

. Example 2 7 Sn Sb Pb 30,000 pounds of antimonial lead were melted Percent Percent v V I in a smelting tt 4260 13.05 Balance The composition of the lead at the start of the operation was: x m 5 v 10,020 pounds of a lead tin alloy resulting from Sn Sb AS Pb the smelting of lead tin alloy residues in a reverberator'y furnace were molten in a melting pot 6 f fg gf g Balance gistgmt skimming the initially formed surface The composition of the molten metal was, as A mixture of 90 pounds of NaOH and 35 pounds follows: sulphur were added as refining agent's. 70

During the work samples of the treated'and Sn S c it I s 1 b stirred metal were poured in a mold and analyzed for the contents of arsenic'in order to follow up Percefit per; cent Percent .Per cent Percent. the progressive action of the reagents. 7 Balance After 30 minutes or work and upon admixture S11 Sb Pb Per cent Per cent 40. 2 8 Balance The dross contained 21.4% tin. If alloys having higher tin and relatively high 8. 8,745 pounds of-refined metal were recovered having the following composition:

Sn Sb Pb Per cent 6. 3 Balance Per cent The above-referred-to variety of examples has been carried-over without previous analysis; this proves that it is possible to work in accordance with this invention without any preliminary steps to identify the character and the quantity of the iron percentages and also containing sulfides are impurities present in the materials which is a refined the metal surface is cleared from the necessary expedient in any hitherto customary dross upon completion of the refining procedure; lead and its alloys refining process. the stirring of the bath must be continued, until The invention has been described with referbrilliant surface of the metal indicates that the ence to a preferred embodiment and it will be metal is pure and no more dross is formed. understood that many variations and modifica- Emample 6 tions thereof may be resorted to without departure from the scope of the invention as de- 10,020 pounds of a lead base alloy derived from fined in the following claims. the smelting of commercial lead base metal What I claim, is: residues in a reverberatory furnace were melted 1. In a method for the collective removal of in a pot. The upper portion of the bath was impurities of copper, nickel, arsenic, iron, sulphur covered with a thickly fluid mush and the refinfrom essentially contaminated lead and lead, tin, ing operation was commenced without removantimony alloys by one and the same operation ing the same. the steps of melting the initial impure metal The composition of the initial metal was: while retaining the dross formed on the surface Sn Sb Cu Ni Ic As S Pb I i arr r? age" t. ear" t. Rance 30 pounds NaOH and 10 pounds S were added; of the metal bath, gradually stirring in the same the metal bath was refined as described above. independently upon the quantity of the said im- 940 pounds dross containing 24.3% Cu were purities a mixture of sodium hydroxide and removed after the completion of the refining sulphur which mixture equals to about 0.3% of procedure and 9,165 pounds of purified metal the weight of the molten charge the ratio of the were recovered having the following composition: said two components being about 2-5 parts of the sodium hydroxide to about 1 part of the sulphur producing hereby a mush compound on $11 Sb Pb the metal which consists of the impurities and adhering metal, continuing the stirring until the F r ggen M 8 B 1 adhering metal is separated from the mush and the latter is transformed into a dross containing the said impurities and removing the dross from Example the refined metal bath.

2. In a method for the collective removal of 9 550 pounds of metal ingots Obtained from impurities of copper, nickel, arsenic,iron, sulphur t smelting of commercial lead base residues from essentially contaminated lead and lead, tin, in a m furnace were melted in a smelting antimony alloys by one and the same operation pot. The refining operation was commenced imthe Steps of melting al mpu e metal medjately upon t liquefaction of t t while retaining the dross formed on the surface The mushy layer formed on the surface of the 0 the metal bath, dually stirrin to the bath was not removed. same independently upon the quantity of the Th composition f the molten m t 1 was, as said impurities a mixture of sodium hydroxide follows; and sulphur which mixture equals to about 0.1

Sn Sb Cu As Fe Ni S Pb Percent Per cent Percent Percent Percent Percent Percent Percent 20 pounds of a mixture of NaOH and 10 pounds S were added and the metal refined in the above described manner.

990 pounds dross containing 35.4% copper were removed at the completion of the refining operation.

to 1% of the weight of the molten charge the ratio of the said two components being about 2-5 parts of the sodium hydroxide to about 1 part of the sulphur producing hereby a mush compound on the metal which consists of the impurities and adhering metal, continuing the stirring until the adhering metal is separated from the mush and the latter is transformed into a dross containing the said impurities and removing the dross from the refined metal bath.

3. In a method for the collective removal of impurities of copper, nickel, arsenic, iron, sulphur from lead, tin, antimony alloys derived from reverberatory and blast furnace smelting processes of low tin containing dresses and residues by one and the same operation the steps of melting the alloy whereby a dross layer is formed on the surface of the molten bath, gradually stirring into the said metal bath while retaining said dross layer and independently upon the quantity of the said impurities a mixture of sodium hydroxide and sulphur which mixture equals to about 0.5% of the weight of the molten charge the ratio of the said two components being about 2-5 parts of the sodium hydroxide to about 1 part of the sulphur producing hereby a mush compound on the metal which consists of the impurities and adhering metal, continuing the stirring, admixing a drying agent selected from the group consisting of saW dust and coal dust to the metal bath and the mush until the adhering metal is separated from the mush and the latter is transformed into a fine pulverulent dross containing the said impurities and removing the dross from the refined metal bath containing the tin at approximately the same ratio as the initial charge.

4. In a method for the collective removal of impurities of copper, arsenic, nickel, iron, sulphur from lead and tin antimony containing white metal alloys the steps of melting the metals 10 while retaining the dross formed on the surface of the metal bath, gradually stirring into the same independently upon the quantity of the said impurities a mixture of sodium hydroxide and sulphur which mixture equals to about 0.3% of the weight of the molten charge the ratio of the said two components being about 2-5 parts of the sodium hydroxide to about 1 part of the sulphur producing hereby a mush compound on the metal which consists of the impurities and adhering metal, continuing the stirring, admixing a dry agent selected from the group consisting of saw dust and coal dust to the metal bath and the mush until the adhering metal is separated from the mush and the latter is transformed into a fine pulverulent dross containing the said impurities and removing the dross from the refined metal bath containing the tin at a higher ratio as in the initial alloys proportionally to the removed impurities.

MAX MEYER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,625,956 Asbeck May 14, 1912 1,386,503 I-Iulst et a1. Aug. 2, 1921 1,594,424 Mulligan Aug. 3, 1925 1,931,285 Colcord Oct. 17, 1933 2,217,981 Hallows Oct. 15, 1940 

2. IN A METHOD FOR THE COLLECTIVE REMOVAL OF IMPURITIES OF COPPER, NICKEL, ARSENIC, IRON, SULPHUR FROM ESSENTIALLY CONTAMINATED LEAD AND LEAD, TIN, ANTIMONY ALLOYS BY ONE AND THE SAME OPERATION THE STEPS OF MELTING THE INITIAL IMPURE METAL WHILE RETAINING THE DROSS FORMED ON THE SURFACE OF THE METAL BATH, GRADUALLY STIRRING INTO THE SAME INDEPENDENLY UPON THE QUANTITY OF THE SAID IMPURITIES A MIXTURE OF SODIUM HYDROXIDE AND SULPHUR WHICH MIXTURE EQUALS TO ABOUT 0.1 TO 1% TO THE WEIGHT OF THE MOLTEN CHARGE THE RATIO OF THE SAID TWO COMPONENTS BEING ABOUT 2-5 PARTS OF THE SODIUM HYDROXIDE TO ABOUT 1 PART OF THE SULPHUR PRODUCING HEREBY A MUSH COMPOUND ON THE MERTAL WHICH CONSISTS OF THE IMPURITIES AND ADHERING METAL, CONTINUING THE STIRRING UNTIL THE ADHERING METAL IS SEPARATED FROM THE MUSH AND THE LATTER IS TRANSFORMED INTO A DROSS CONTAINING THE SAID IMPURITIES AND REMOVING THE DROSS FROM THE REFINED METAL BATH. 